1. Field of the Invention
The present invention relates to a method of forming a pattern, and more particularly, to a method of forming a fine pattern having a width of at most 0.2 .mu.m by forming two resist layers.
2. Description of the Background Art
In order to process a layer required to be processed, an insulating film, for example, in forming a semiconductor device, a method of forming a resist pattern of a single resist layer and processing an insulating film according to the resist pattern is generally used. In order to process an insulating film having many stepped portions, however, a method of forming a first resist layer as a flattening layer on the insulating film, forming a second resist layer on the first resist layer, and forming a resist pattern in the second resist layer has been often used. The methods disclosed in the following documents (i) to (vii) have been known as such a method of forming a pattern using two resist layers.
(i) J. Vac. Sci. Technol., B11(6), November/December 1993, pp. 2789.about.2793(1993) PA1 (ii) J. Vac. Sci. Technol., B12(6), November/December 1994, pp. 3919.about.3924(1994) PA1 (iii) J. Vac. Sci. Technol., B13(6), November/December 1995, p. 2366.about.2371 (1995) PA1 (iv) SPIE, Vol. 2438, pp. 762.about.774 (1995) PA1 (v) SPIE, Vol. 2437, pp. 308.about.330 (1995) PA1 (vi) Japanese Patent Laying-Open No. 3-188447 PA1 (vii) Japanese Patent Laying-Open No. 4-301646 PA1 (i) forming a first layer by applying an organic material on a layer to be processed; PA1 (ii) forming a second layer having a thickness in the range from 30 to 100 nm by applying a material which can be treated with an organic metal reagent on the first layer, wherein organic metal is metal which has been bonded to carbon and the metal includes silicon; PA1 (iii) selectively forming in the second layer a portion which cannot be treated with an organic metal reagent; PA1 (iv) treating with an organic metal reagent the second layer except the portion which cannot be treated with an organic metal reagent; and PA1 (v) removing the portion which cannot be treated with an organic metal reagent and a portion of the first layer which is located thereunder. PA1 (i) forming a first layer by applying an organic material on a layer to be processed; PA1 (ii) forming a second layer having a thickness in the range from 30 to 100 nm by applying a material which can be treated with an organic metal reagent on the first layer; PA1 (iii) selectively directing light to the second layer; PA1 (iv) turning a portion of the second layer which has been exposed to the light into a portion which cannot be treated with an organic metal reagent by heating the second layer; PA1 (v) treating with an organic metal reagent the second layer except the portion which cannot be treated with an organic metal reagent; and PA1 (vi) removing the portion which cannot be treated with an organic metal reagent and a portion of the first layer which is located thereunder. PA1 (i) forming a first layer by applying an organic material on a layer to be processed; PA1 (ii) forming a second layer having a thickness in the range from 30 to 100 nm by applying a material which can be treated with an organic material reagent on the first layer; PA1 (iii) selectively directing light to the second layer to turn a portion of the second layer which has been exposed to the light into a portion which cannot be treated with an organic metal reagent; PA1 (iv) treating with an organic metal reagent the second layer except the portion which cannot be treated with an organic metal reagent; and PA1 (v) removing the portion which cannot be treated with an organic metal reagent and a portion of the first layer which is located thereunder. PA1 (i) forming a first layer by applying a first organic material on a layer to be processed; PA1 (ii) forming a second layer having a thickness in the range from 30 to 100 nm by applying a second organic material on the first layer; PA1 (iii) selectively forming in the second layer a portion which can be treated with an organic metal reagent; PA1 (iv) treating with an organic metal reagent the portion which can be treated with an organic metal reagent; and PA1 (v) removing the second layer except the portion which can be treated with an organic metal reagent and a portion of the first layer which is located under the second layer except the portion which can be treated with an organic metal reagent. PA1 (i) forming a first layer by applying a first organic material on a layer to be processed; PA1 (ii) forming a second layer having a thickness in the range from 30 to 100 nm by applying a second organic material on the first layer; PA1 (iii) selectively directing light to the second layer to turn a portion of the second layer which has been exposed to the light into a portion which can be treated with an organic metal reagent; PA1 (iv) turning the second layer except the portion which can be treated with an organic metal reagent into a portion which cannot be treated with an organic metal reagent by heating the second layer; PA1 (v) treating with an organic metal reagent the portion which can be treated with an organic metal reagent; and PA1 (vi) removing the portion which cannot be treated with an organic metal reagent and a portion of the first layer which is located thereunder. PA1 (i) forming a first layer by applying a first organic material on a layer to be processed; PA1 (ii) forming a second layer having a thickness in the range from 30 to 100 nm by applying a second organic material on the first layer; PA1 (iii) selectively directing light to the second layer; PA1 (iv) turning a portion of the second layer which has been exposed to the light into a portion which can be treated with an organic metal reagent by heating the second layer; PA1 (v) treating with an organic metal reagent the portion which can be treated with an organic metal reagent; and PA1 (vi) removing the second layer except the portion which can be treated with an organic metal reagent and a portion of the first layer which is located under the second layer except the portion which can be treated with an organic metal reagent. PA1 (i) forming a first layer by applying a first organic material on a layer to be processed; PA1 (ii) forming a second layer having a thickness in the range from 30 to 100 nm by applying a second organic material on the first layer; PA1 (iii) turning the entire second layer into a layer which can be treated with an organic metal reagent; PA1 (iv) selectively directing light to the second layer which can be treated with an organic metal reagent to turn a portion of the second layer which has been exposed to the light into a portion which cannot be treated with an organic metal reagent; PA1 (v) treating with an organic metal reagent the portion of the second layer which can be treated with an organic metal reagent; and PA1 (vi) removing the portion which cannot be treated with an organic metal reagent and a portion of the first layer which is located thereunder.
The methods disclosed in the documents (i) to (v) will now be described in conjunction with the accompanying drawings.
FIGS. 55 to 60 are cross sectional views showing a conventional method of forming a pattern.
Referring to FIG. 55, a lower resist layer 302 is formed as a flattening layer on a layer 301 to be processed.
Referring to FIG. 56, an upper resist layer 303 is formed on a surface of lower resist layer 302. Since the surface of lower resist layer 302 is flat, upper resist layer 303 has an almost uniform thickness (0.20 to 0.22 .mu.m).
Referring to FIG. 57, light with a wavelength of 248 nm shown by arrows 304 is directed to upper resist layer 303, whereby upper resist layer 303 partially becomes an exposed region 305.
Referring to FIG. 58, upper resist layer 303 and exposed region 305 in FIG. 57 are heated, whereby a layer 306 which cannot be silylated (hereinafter referred to as un-silylatable layer) and a layer 307 which can be silylated (hereinafter referred to as silylatable layer) are formed.
Referring to FIG. 59, un-silylatable layer 306 and silylatable layer 307 in FIG. 58 are made in contact with gas containing silicon atoms, whereby silylatable layer 307 is turned into a silylated layer 308.
Referring to FIG. 60, un-silylatable layer 306 and lower resist layer 302 located thereunder in FIG. 59 are etched with oxygen plasma shown by arrows 310. On the other hand, a surface of silylated layer 308 reacts with oxygen plasma shown by the arrows 310 to be an oxide film 309. This oxide film 309 serves as a shielding film against oxygen plasma. Therefore, silylated layer 308 and lower resist layer 302 located thereunder will not be etched.
A conventional pattern is thus formed.
In recent years, elements constituting a semiconductor device have been miniaturized. In addition, with increase in the integration degree of a semiconductor device, a pattern formed in resist has been required to be so fine as to have a width of at most 0.20 .mu.m. Problems which occur when such a fine pattern is formed by a conventional method will now be described.
FIGS. 61 to 64 are cross sectional views illustrating a conventional method of forming a fine pattern. Referring to FIG. 61, a lower resist layer 302 is formed as a flattening layer on a layer 301 to be processed. An upper resist layer 303 having a thickness in the range from 0.20 to 0.22 .mu.m is formed on lower resist layer 302. Light with a wavelength of 248 nm shown by arrows 304 is directed to a portion of upper resist layer 303, whereby an exposed region 305 is formed. A width (W.sub.1 in the figure) of exposed region 305 is at most 0.20 .mu.m. Furthermore, a distance (W.sub.2 in the figure) between exposed regions 305 is also at most 0.20 .mu.m.
Referring to FIG. 62, upper resist layer 303 and exposed region 305 in FIG. 61 are heated, whereby an un-silylatable layer 306 and a silylatable layer 307 are formed.
Referring to FIG. 63, un-silylatable layer 306 and silylatable layer 307 in FIG. 62 are made in contact with gas containing silicon atoms, whereby silylatable layer 307 is turned into a silylated layer 308. At this time, silylated layer 308 swells. If a distance between silylated layers 308 is large, swelling of silylated layers 308 will not cause problems. When the distance between silylated layers 308 is at most 0.20 .mu.m, however, silylated layers 308 join with each other as a result of swelling as shown in FIG. 63.
Referring to FIG. 64, since silylated layers 308 join with each other, a portion of lower resist layer 302, which should be etched away, remains unetched, so that a desired pattern cannot be formed.
Furthermore, as shown in FIG. 63, silylated layer 308 is thicker in the center thereof and becomes thinner towards the end thereof as a result of swelling. Therefore, the end of silylated layer 308 might be etched during dry etching by oxygen plasma. The end of silylated layer 308 might not be etched. The size of a pattern in the case where the end of silylated layer 308 is etched is a different from that in the case where the end of silylated layer 308 is not etched on a nanometer order.
If the size of a pattern is large, such an error on a nanometer order will not cause problems, but when a resist pattern having a size of at most 0.20 .mu.m is to be formed, such an error on a nanometer order will cause problems.
In addition, a conventional method of forming a pattern causes other problems. FIG. 65 is a cross sectional view used for illustration of reflection (halation) of light from a stepped portion of a layer to be processed. Referring to FIG. 65, a lower resist layer 302 is formed on a layer 301 to be processed. An upper resist layer 303 is formed on lower resist layer 302. Light shown by arrows 304 in the figure is directed to a portion of upper resist layer 303, whereby an exposed region 305 is formed. At this time, light shown by the arrow 304 is reflected by a stepped portion of layer 301. Therefore, a region 330 which should not be exposed to light is exposed to light, so that a desired pattern cannot be formed.